Mining Magneto Wall Telephone
Designed substantially and specially for use in mines and where the conditions are detrimental to ordinary type telephones.
Explosion-proof and watertight, complies with the Home Office recommendations for safety in mines.
The apparatus in the inner compartment is sealed by the inner door, which is fastened by heavy machine screws, arranged for attaching a seal, if desired.
The cut-out on the generator is totally enclosed, making it absolutely impossible for open sparking to take place.
The outer door, fitted with a slam catch, makes the case quite watertight and protects the speaking equipment from mechanical damage and dirt.
Two all-metal receivers with flexible arms and the transmitter are mounted as an integral unit, and when raised for use automatically operates the switch for connecting the speaking battery.
Transmitter: Interchangeable "Inset" type protected by moisture-proof shield and metal grid.
Generator: 2 special large section magnets equal to 5 of the ordinary size.
Ringer: 2000 ohms with the hammer operating (through a gland) between two extra large gongs which are well protected.
Dry cells are included.
The terminals for the line, extension bell or relay and also for external speaking battery, if desired, are mounted at the bottom of the case in a separate compartment which may be sealed with a suitable compound. The speaking battery is normally fitted in the inner compartment.
The apparatus, coil windings and wiring are specially treated to prevent the detrimental and corrosive effects of moisture and gases, etc.
A diagram of the connections is supplied with each instrument.
N2980 was introduced in 1921.
|Code No.||Description||Weight||Certified for|
|N2980||cast-iron case||80 lb||Pairs only|
|N2981||aero-engine quality aluminium case||41 lb||Parallel|
|N2982||cast-iron||80 lb||Pairs only|
|N2983||aero-engine quality aluminium case||40 lb||Parallel|
Height 16.5 inches
Width 13.5 inches
Depth 10 inches
NOTE - Mining switchboard N515 is suitable for use with these
Taken from the Ericsson catalogue, edition 26
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